filterinputstream.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 244 行

/*
 * @(#)FilterInputStream.java	1.30 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.io;

/**
 * A <code>FilterInputStream</code> contains
 * some other input stream, which it uses as
 * its  basic source of data, possibly transforming
 * the data along the way or providing  additional
 * functionality. The class <code>FilterInputStream</code>
 * itself simply overrides all  methods of
 * <code>InputStream</code> with versions that
 * pass all requests to the contained  input
 * stream. Subclasses of <code>FilterInputStream</code>
 * may further override some of  these methods
 * and may also provide additional methods
 * and fields.
 *
 * @author  Jonathan Payne
 * @version 1.23, 02/02/00
 * @since   JDK1.0
 */
public
class FilterInputStream extends InputStream {
    /**
     * The input stream to be filtered. 
     */
    protected InputStream in;

    /**
     * Creates a <code>FilterInputStream</code>
     * by assigning the  argument <code>in</code>
     * to the field <code>this.in</code> so as
     * to remember it for later use.
     *
     * @param   in   the underlying input stream, or <code>null</code> if 
     *          this instance is to be created without an underlying stream.
     */
    protected FilterInputStream(InputStream in) {
	this.in = in;
    }

    /**
     * Reads the next byte of data from this input stream. The value 
     * byte is returned as an <code>int</code> in the range 
     * <code>0</code> to <code>255</code>. If no byte is available 
     * because the end of the stream has been reached, the value 
     * <code>-1</code> is returned. This method blocks until input data 
     * is available, the end of the stream is detected, or an exception 
     * is thrown. 
     * <p>
     * This method
     * simply performs <code>in.read()</code> and returns the result.
     *
     * @return     the next byte of data, or <code>-1</code> if the end of the
     *             stream is reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public int read() throws IOException {
	return in.read();
    }

    /**
     * Reads up to <code>byte.length</code> bytes of data from this 
     * input stream into an array of bytes. This method blocks until some 
     * input is available. 
     * <p>
     * This method simply performs the call
     * <code>read(b, 0, b.length)</code> and returns
     * the  result. It is important that it does
     * <i>not</i> do <code>in.read(b)</code> instead;
     * certain subclasses of  <code>FilterInputStream</code>
     * depend on the implementation strategy actually
     * used.
     *
     * @param      b   the buffer into which the data is read.
     * @return     the total number of bytes read into the buffer, or
     *             <code>-1</code> if there is no more data because the end of
     *             the stream has been reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#read(byte[], int, int)
     */
    public int read(byte b[]) throws IOException {
	return read(b, 0, b.length);
    }

    /**
     * Reads up to <code>len</code> bytes of data from this input stream 
     * into an array of bytes. This method blocks until some input is 
     * available. 
     * <p>
     * This method simply performs <code>in.read(b, off, len)</code> 
     * and returns the result.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset of the data.
     * @param      len   the maximum number of bytes read.
     * @return     the total number of bytes read into the buffer, or
     *             <code>-1</code> if there is no more data because the end of
     *             the stream has been reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public int read(byte b[], int off, int len) throws IOException {
	return in.read(b, off, len);
    }

    /**
     * Skips over and discards <code>n</code> bytes of data from the 
     * input stream. The <code>skip</code> method may, for a variety of 
     * reasons, end up skipping over some smaller number of bytes, 
     * possibly <code>0</code>. The actual number of bytes skipped is 
     * returned. 
     * <p>
     * This method
     * simply performs <code>in.skip(n)</code>.
     *
     * @param      n   the number of bytes to be skipped.
     * @return     the actual number of bytes skipped.
     * @exception  IOException  if an I/O error occurs.
     */
    public long skip(long n) throws IOException {
	return in.skip(n);
    }

    /**
     * Returns the number of bytes that can be read from this input 
     * stream without blocking. 
     * <p>
     * This method
     * simply performs <code>in.available()</code> and
     * returns the result.
     *
     * @return     the number of bytes that can be read from the input stream
     *             without blocking.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public int available() throws IOException {
	return in.available();
    }

    /**
     * Closes this input stream and releases any system resources 
     * associated with the stream. 
     * This
     * method simply performs <code>in.close()</code>.
     *
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public void close() throws IOException {
	in.close();
    }

    /**
     * Marks the current position in this input stream. A subsequent 
     * call to the <code>reset</code> method repositions this stream at 
     * the last marked position so that subsequent reads re-read the same bytes.
     * <p>
     * The <code>readlimit</code> argument tells this input stream to 
     * allow that many bytes to be read before the mark position gets 
     * invalidated. 
     * <p>
     * This method simply performs <code>in.mark(readlimit)</code>.
     *
     * @param   readlimit   the maximum limit of bytes that can be read before
     *                      the mark position becomes invalid.
     * @see     java.io.FilterInputStream#in
     * @see     java.io.FilterInputStream#reset()
     */
    public synchronized void mark(int readlimit) {
	in.mark(readlimit);
    }

    /**
     * Repositions this stream to the position at the time the 
     * <code>mark</code> method was last called on this input stream. 
     * <p>
     * This method
     * simply performs <code>in.reset()</code>.
     * <p>
     * Stream marks are intended to be used in
     * situations where you need to read ahead a little to see what's in
     * the stream. Often this is most easily done by invoking some
     * general parser. If the stream is of the type handled by the
     * parse, it just chugs along happily. If the stream is not of
     * that type, the parser should toss an exception when it fails.
     * If this happens within readlimit bytes, it allows the outer
     * code to reset the stream and try another parser.
     *
     * @exception  IOException  if the stream has not been marked or if the
     *               mark has been invalidated.
     * @see        java.io.FilterInputStream#in
     * @see        java.io.FilterInputStream#mark(int)
     */
    public synchronized void reset() throws IOException {
	in.reset();
    }

    /**
     * Tests if this input stream supports the <code>mark</code> 
     * and <code>reset</code> methods. 
     * This method
     * simply performs <code>in.markSupported()</code>.
     *
     * @return  <code>true</code> if this stream type supports the
     *          <code>mark</code> and <code>reset</code> method;
     *          <code>false</code> otherwise.
     * @see     java.io.FilterInputStream#in
     * @see     java.io.InputStream#mark(int)
     * @see     java.io.InputStream#reset()
     */
    public boolean markSupported() {
	return in.markSupported();
    }
}